22/7 wrote:The twins experiment has to do with an object (or person) moving at nearly the speed of light and the effects that that difference in velocity will have on that object (or person). I don't believe that acceleration comes into play, but rather relative velocities.

But the "paradox" comes from the fact that the now-younger (the one that left and came back) could claim by the equivalence principle that he was the one who stayed still, while everything else moved away from him and his ship and then came back. So, he asks, why is he younger while his brother has aged?

This is resolved by the fact that the travelling twin accelerated and decelerated. The reference frames are not always equivalent, and the travelling twin's frame isn't always inertial. Therefore he can't make such a claim.

Sure, but when you're designing something based on whether or not it accelerating, you're assuming an inertial reference frame, since we're never approaching the speed of light. So arguing that it's not provable whether or not the feather is accelerating is kind of pointless, and if you start looking at all such situations in the same light (is that person actually turning left? can I prove that?) then you'll never do anything.

Totally not a hypothetical...

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22/7 wrote:The twins experiment has to do with an object (or person) moving at nearly the speed of light and the effects that that difference in velocity will have on that object (or person). I don't believe that acceleration comes into play, but rather relative velocities.

But the "paradox" comes from the fact that the now-younger (the one that left and came back) could claim by the equivalence principle that he was the one who stayed still, while everything else moved away from him and his ship and then came back. So, he asks, why is he younger while his brother has aged?

This is resolved by the fact that the traveling twin accelerated and decelerated. The reference frames are not always equivalent, and the traveling twin's frame isn't always inertial. Therefore he can't make such a claim.

(I fixed a Traveling spelling error according to Firefox there.)I agree. You cannot make any such claims about anything anywhere near Newtonian-based without and inertial reference frame, because all of Newton's principles were based upon inertial frames. The basic premise of the acceleration argument is based on Newton's F=MA. For that matter, Velocity is arguably a Newtonian concept. And even if you added in the relativity adjustment, you still need inertial reference frames for the equation to hold true.

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Remove all strands from the feather to leave only the central shaft, measure it's length, secure each end and apply a known tension. Subject the shaft to sound waves at various known frequencies until you find the fundamental harmonic of the feather, deduce the mass/unit length (linear mass).Repeat above for one (or more) of the removed strands, multiply the shaft's/strand's linear mass by their respective lengths and sum the result.

Now, since feathers are used for flying, they go up and not down in a gravitational field [the earth]. This means that they have negative mass. So the correct way to find the mass is to hold a scale upside down and let a feather go underneath it. QED.

necroforest wrote:Uh, you're all really wrong. I would have expected better of you.

Now, since feathers are used for flying, they go up and not down in a gravitational field [the earth]. This means that they have negative mass. So the correct way to find the mass is to hold a scale upside down and let a feather go underneath it. QED.

Well, obviously, but that does not cover all possible feathers. What if it came from a flightless bird?

Negative mass, you say? That arises the obvious question of how? I propose that there is some sort of graviton, only opposite; an antigraviton, if you will (yeah, I know, just hear me out.) This is a particularly utile notion in that it finally solves the bumblebee problem; although they are too heavy to fly, their antigraviton glands allow them to defy those calculations and spit in the faces of apiarists and entomologists everywhere.

Nonono. You're all wrong. Feathers go up AND down. That means the mass CHANGES. It's positive sometimes, and negative other times. That means they average out to have zero mass. Now to satisfy the science, remember this is only true when the bird is staying at a constant altitude. If the bird is increasing altitude, then the feathers are going up more than they go down, so it must have a negative average mass. This must be related to the feather moving to different distances from Earth and experiencing different gravities. As we get further away from Earth, the gravitational force decreases, and at the same time the feathers have negative mass. Now, obviously, the magnitude of the feather's mass is proportional to the rate of change of the gravitational force.

So, if you place it on a balance, it will have zero mass. If, however, you give it some initial force downwards, then it will begin to have positive mass and begin to accelerate onto the scale. Until it hits the scale, then it will push the scale down, and the scale will read a certain mass. Then, since the feather has stopped moving through earth's gravity field, its mass will zero out, and the scale will no longer be held down: It will push the feather up. Then it will have negative mass. It will continue to accelerate upwards due to the negative acceleration due to gravity until it hits something (like an upside down scale), or leaves the pull of earth's gravity completely, say by traveling through a wormhole to an alternate universe where there is no pull of gravity. (This universe could, hypothetically, be filled with massless feathers. As soon as they encounter a moving gravitational field, however, the feathers will all have a mass and will begin to move opposite the direction of the gravitational field.)

Gowerly wrote:Smoosh the feather into something of uniform and known density, measure the volume (water displacement, obviously), and divide!

But don't feathers trap a lot of air when submerged? Maybe "trap" isn't the best way to describe it, but some parts of the feather are mildly hydrophobic, and those overlapping parts tend to hold miniscule amounts of air. Which, i suppose, is why a feather floats to the top of a bucket of water even if you squish it around at the bottom for a while. So...wouldn't that skew the results and give you a screwed-up density? You'll have to somehow make sure that there is no air left in whatever shape you "smoosh the feather into."

Cue personal crazy idea:Ultimately, the definition of "feather" is unaddressed. Does it have to be natural? Can it be synthetic?Because then you could construct a feather of arbitrarily large size (carbon nanotubes ftw!), and mass it somewhere convenient in orbit around Jupiter.

Suspend the feather a known distance above the earth. Then, you can find the gravitational force that the feather exerts on the earth. The earth is big, so this should be easier than measuring the weight of something as small as a feather. You could put a spring scale upside down on the floor, and measure the difference in the reading between when the feather is at the same level as the scale (thus not pulling vertically on the scale) and when the feather is at the known height. Since we know the mass of the earth, too, we can use Newton's law of gravitation to find the mass of the feather.

First, you should measure the gravitational acceleration on the surface of Earth. In order not to mess with relativity, let's just say [imath]g=\frac{GM}{R^2}[/imath]. Just put your scales upside-down, measure the mass of the Earth, get a ruler, measure the maximum circle of the planet. Assuming the Earth is a sphere, divide it by [imath]2\pi[/imath]. Put it all in the formula, and you have found g.

Now get yourself a wind tunnel. Determine the drag coefficient of the feather (I'm not going into details on how to do it).

Now let the feather fall, until it reaches its terminal speed. Measure it. In this case, gravity equals drag. Accordingly: [imath]m.g = b.v[/imath]

J Spade wrote:Uh, weigh the feather in Newtons, divide by the local acceleration due to gravity.

That would never work.

Explain please? I just began physics this year. As far as I know, it would work.

I think the point is, your solution makes too much sense. We can't be having any of that around here.

Perhaps if we put the feather at an arbitrary point in space, between our system and a nearby star, and then measure the subtle gravitational lensing effect. From that we could derive the mass based on the slight change in curvature of local space-time. That would be much easier.

ST47 wrote:Nonono. You're all wrong. Feathers go up AND down. That means the mass CHANGES. It's positive sometimes, and negative other times. That means they average out to have zero mass. Now to satisfy the science, remember this is only true when the bird is staying at a constant altitude. If the bird is increasing altitude, then the feathers are going up more than they go down, so it must have a negative average mass. This must be related to the feather moving to different distances from Earth and experiencing different gravities. As we get further away from Earth, the gravitational force decreases, and at the same time the feathers have negative mass. Now, obviously, the magnitude of the feather's mass is proportional to the rate of change of the gravitational force.

So, if you place it on a balance, it will have zero mass. If, however, you give it some initial force downwards, then it will begin to have positive mass and begin to accelerate onto the scale. Until it hits the scale, then it will push the scale down, and the scale will read a certain mass. Then, since the feather has stopped moving through earth's gravity field, its mass will zero out, and the scale will no longer be held down: It will push the feather up. Then it will have negative mass. It will continue to accelerate upwards due to the negative acceleration due to gravity until it hits something (like an upside down scale), or leaves the pull of earth's gravity completely, say by traveling through a wormhole to an alternate universe where there is no pull of gravity. (This universe could, hypothetically, be filled with massless feathers. As soon as they encounter a moving gravitational field, however, the feathers will all have a mass and will begin to move opposite the direction of the gravitational field.)

What do they teach you all these days?

Your theory is fundamentally flawed because we obviously won't have a balance between the number of feathers going up and the number of feathers going down. What happens if we have birds that begin their lives at a lower altitude and then migrate to a higher altitude? This is more likely to happen over time due to an increase in the sea level and forced changes in migratory patterns due to global climate change.

I feel a full-scale, massively overfunded inquisition into the migratory patterns of every bird on the planet is the most efficient course of action. We will split into two groups of infinity people each; the first group is responsible for measuring every altitude change of every bird on Earth over the course of several million years and the second group is responsible for painstakingly plucking all the feathers from each bird in order to find the average mass of all the feathers in the world, which I believe is going to be slightly larger than zero.

Hi friend, Why did you ask the question " what is the mass of a feather? " ? Don' t you think it is a silly question. And why do you want to know the mass of a feather? All right friend, I will answer your question. Look at following!

If you really want to know the mass of a feather,

Firstly, you have to know the equation: w=mg . Do you know ? Well , if you know , let's start our calculation !Secondly,let the weight of your feather be 0.00000000001 N.So, we can calculate by using the equation: m= w/g . mass of the feather = 0.00000000001/10

Accordingly, m = 0.0000000001 kg

To be concluded, the mass of your feather may be 0.0000000001 kg if yours is 0.00000000001 N weighs. If not , you can calculateby using the above equation w= mg .

sherlock holmes wrote:Hi friend,Why did you ask the question " what is the mass of a feather? " ? Don' t you think it is a silly question. And why do you want to know the mass of a feather? All right friend, I will answer your question. Look at following!

If you really want to know the mass of a feather,

Firstly, you have to know the equation: w=mg . Do you know ? Well , if you know , let's start our calculation !Secondly,let the weight of your feather be 0.00000000001 N.So, we can calculate by using the equation: m= w/g .mass of the feather = 0.00000000001/10

Accordingly, m = 0.0000000001 kg

To be concluded, the mass of your feather may be 0.0000000001 kg if yours is 0.00000000001 N weighs. If not , you can calculateby using the above equation w= mg .

Goodbye ! See you later on xkcd website . Bye now

No shit, Sherlock!

Get it? 'Cause he totally missed the point and his name is sherlock holmes and...

Spoiler:

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I think the best way would be to find a cosmic string. To the string, attach a magnetic monopole on one end and a naked singularity on the other. Excite the string with the feather. Count how many universes are spawned. Then find the energy in each of these universes. Since the total energy comes from the feather motion, use the kinetic energy to find the mass. This would require measuring the velocity, though, and that might be tricky.